Ruxolitinib targets JAK-STAT signaling to modulate neutrophil activation in refractory macrophage activation syndrome

ABSTRACT: Macrophage activation syndrome (MAS) is believed to be caused by inappropriate proliferation and activation of the mononuclear phagocytic system. Adult-onset Still disease (AOSD) is characterized by neutrophil activation and a cytokine storm, which can lead to the severe and potentially life-threatening complication of MAS. RNA sequencing revealed that neutrophils may play a distinct role and enhance the innate immunity of patients with AOSD with MAS (AOSD-MAS). In the CpG-induced secondary hemophagocytic lymphohistiocytosis (HLH) model, the depletion of neutrophils significantly reduced cytokine levels with effects comparable with monocyte depletion. Significant enrichment was observed in the type I/II interferon and JAK-STAT pathways in neutrophils from patients with AOSD-MAS. Treatment of 10 patients with refractory AOSD-MAS with ruxolitinib led to the resolution of inflammatory parameters and clinical symptoms. RNA sequencing and ex vivo assays confirmed that ruxolitinib suppressed aberrant NETosis and STAT3/STAT5 signaling. In vivo, PAD4 knockout further confirmed the pathogenic role of NETosis in a secondary HLH model. Moreover, the selective inhibition of STAT3 or STAT5 alleviated systemic inflammation. Ten functional variants were identified in genes related to the JAK-STAT pathway, however, their clinical relevance requires further validation. These findings suggest that ruxolitinib has the potential to facilitate disease remission in patients with refractory AOSD-MAS by broadly inhibiting JAK-STAT signaling and modulating neutrophil activation and NETosis.